A recent trend is to evolve road-to-vehicle or vehicle-to-vehicle communication for the purpose of reducing traffic accident fatalities and promoting preventive safety. It is important for the preventive safety to ensure message integrity because an incorrect message is highly likely to cause a serious accident. For example, it is important to ensure that a message is transmitted from a correct roadside device or a correct vehicle-mounted terminal and that a malicious user does not falsify the message transmitted from a correct roadside device or a correct vehicle-mounted terminal.
The electronic signature using a public key encryption system ensures message validity. The public key encryption system performs encryption and decryption using a pair of two keys, a private key and a public key. The private key needs to be secretly managed. The public key may be made public. The electronic signature using the public key encryption system is equivalent to data resulting from encrypting a hash value for the message based on the private key. A message sender transmits the message along with the signature. A message recipient acquires the sender's public key and decrypts the signature. The message recipient verifies the signature by determining whether the decrypted value equals a hash value generated from the received message.
Verifying the public key validity is important for the electronic signature using the public key encryption. Generally, a certificate authority supplies the signature to the public key. If the certificate authority is hierarchically structured, a high-order certificate authority supplies the signature to the public key for a low-order certificate authority and this is repeated.
The signature verification for messages is repeated and is therefore time-consuming. The following patent document discusses the scheme compliant with a system that requires high-speed signature verification for communication with a fast moving vehicle.